Corals Are Retreating From Equator, Study

AsianScientist (Dec. 17, 2012) - A team of international marine scientists warns that corals could retreat from equatorial seas and oceans as the Earth continues to warm.

Working on clues in the fossil coral record from the last major episode of global warming, the researchers found evidence of a sharp decline in equatorial coral diversity between the last two ice ages about 125,000 years ago.

"When the climate warmed rapidly during the Last Interglacial, coral species diversity was much lower close to the Equator than at higher latitudes," said Professor John Pandolfi of CoECRS and The University of Queensland.

"It appears that during this period the number of coral species present in equatorial oceans was only 50-60 percent of the diversity found further away from the equator, and diversity was greatest in the northern hemisphere," he said.

Pandolfi and colleagues found that when sea surface temperatures warmed by about 0.7 degree celsius during the interglacial warm period, it was enough to drive many species of coral out of equatorial waters up to 10 degrees of latitude on either side of the equator.

"Our results suggest that the poleward range expansions of reef corals occurring with intensified global warming today may soon be followed by equatorial range retractions," said the team in their research paper published in the Proceedings of the US National Academy of Sciences.

What concerns the scientists is that the planet has already warmed by 0.7 of a degree since the start of the industrial age – a similar amount to the last interglacial - and while the corals have not yet abandoned equatorial waters, modern equatorial diversity is lower compared to adjacent latitudes north and south.

A drop in equatorial coral diversity has serious implications for the nations of the Coral Triangle, such as Indonesia and the Philippines, where tens of millions of people rely upon the oceans for their livelihoods and food, says Pandolfi.

"The picture that is forming is one of corals moving back and forth, towards the poles during warm periods, and retracting towards the equator in cooler times, in search of the most favorable water conditions," he explained. "It is going to be important to factor this kind of dynamism into how we manage them in the hot times which we now know lie ahead."